1. Field of the Invention
The present invention relates to a system for controlling electromotive force of a motor of an electric vehicle such that precharge is controlled when electric power is supplied to a motor of the electric vehicle.
The present application is based on Japanese Patent Application No. Hei. 11-52036, which is incorporated herein by reference.
2. Description of the Related Art
FIG. 3 is a schematic diagram showing a switching circuit for turning a driving motor of an electric vehicle on. Electric power is supplied to a driving motor 5 from a power source 4 through a power supply line, the power source 4 comprising a mounted battery, which is a load and which is arranged to produce output voltage VB of 400 V. The driving motor 5 is turned on by turning the mechanical main relay 6 on. Since a motor controller 7 for controlling the driving motor 5 contains a capacitor, a great current rapidly flows when the rotation of the driving motor 5 is started. Therefore, there arises a problem in that the fuse is blown or the electrode of the main relay 6 sustains damage.
To overcome the above-mentioned problem, a precharge circuit incorporating a precharge relay 8, which is also a mechanical relay, and a charge resistor 9 is, in parallel, connected to a positive electric line of the power source 4 for supplying electric power. That is, the precharge circuit is turned on in a first stage of start of the driving motor 5 to supply a small electric current controlled by the charge resistor 9 to the motor controller 7 for several seconds. Then, the precharge circuit is turned off, and the main relay 6 is switched on. Thus, the problem caused from rapid supply of a large current can be prevented.
As an alternative to the relay incorporating the mechanical contact, an intelligent-power switch unit (hereinafter abbreviated to xe2x80x9cIPSxe2x80x9d) has been employed in recent years. The IPS is a switching circuit incorporating a semiconductor switching device exhibiting advantageous characteristic. Since the IPS has a self-protective function against abnormality, such as overcurrent, overheat, or the like, the IPS has been employed as a substitute for the mechanical precharge circuit configured as shown in FIG. 3. For example, such a unit has been disclosed in Unexamined Japanese Patent Publication No. Hei. 9-331625.
The disclosed unit incorporates an abnormal-signal output portion arranged to detect the level of the voltage output from a semiconductor switch device. The unit interrupts an excessively large electric current caused from short circuit or the like and issues an alarm of abnormality caused from a small current or overheat occurring owing to opening. Thus, the harness and the system units can effectively be protected.
The IPS supplies voltage to a semiconductor switch device, such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), through an input terminal. The MOSFET is turned on/off in response to an ON/OFF signal output from a drive circuit (a driver). The IPS incorporates an overvoltage detecting circuit for detecting overvoltage when the power supply voltage has been brought to the overvoltage state. Moreover, the IPS incorporates a current detecting circuit for detecting overcurrent by making a comparison between the voltage level caused from the value of an electric current which flows between the drain and the source of the MOSFET and a reference voltage generated by a reference voltage generating circuit. In addition, the IPS incorporates a temperature detecting circuit for detecting overheat of the MOSFET. Detection signals output from the detection circuits are supplied to a NOR circuit or the like. An output signal from the NOR circuit is supplied to the device circuit and a booster circuit (a charge pump circuit). The charge pump circuit is required to raise the voltage level of the gate of the MOSFET when the MOSFET is employed on a high-side in the upstream portion of the load, such as an audio unit. The charge pump circuit is a circuit for raising the output voltage of the battery to output the voltage to the drive circuit as the drive voltage so as to drive the MOSFET. In general, the charge pump circuit is provided for each MOSFET.
However, there is a possibility that the driving-motor switching circuit for an electric vehicle shown in FIG. 3 encounters the following problems which should be solved.
Since both of the main relay 6 and the precharge relay 8 are mechanical relays, the cost and size of each relay cannot easily be reduced.
There arises another problem caused from control of the flow of a large electric current by using the charge resistor 9 having resistance value R which is, for example, 10 ohms (xcexa9). Since the charge resistor 9 cannot be omitted from the circuit, the size of the precharge circuit cannot easily be reduced.
Another problem will now be described. As an alternative to the mechanical relay, a MOS (Meal Oxide Semiconductor) FET (Field Effect Transistor) comprising a semiconductor switch device may be employed. When a rush current flows when electric power is supplied to the driving motor 5 which is the load, there is apprehension that breakdown of the MOSFET occurs. Therefore, also the charge resistor 9 is required when the MOSFET is employed to serve as the switching device. Thus, the size of the precharge circuit cannot satisfactorily be reduced.
Taking excellent characteristics of the IPS into consideration, an object of the present invention is to provide a system for controlling electromotive force of a motor of an electric vehicle, in which, in a switching circuit making a driving motor of the electric vehicle start, an IPS utilizing a semiconductor switching device is employed as a substitute for a precharge circuit having mechanical relays and charge resistors, thereby effectively protecting units by limiting overcurrent occurring when the system is started and permitting cost and size reduction.
To achieve the above object, according to the first aspect of the present invention, there is provided a system for controlling electromotive force of a motor of an electric vehicle, which comprises a motor controller connected to a power supply through a power supply line, and connected to a driving motor which is a load of the power supply, wherein electric power is supplied to the driving motor from the power supply through the motor controller, the motor controller having a capacitor, a main relay inserted in the power supply line to be disposed between the power supply and the motor controller, and a precharge device connected to the power supply line so that the precharge device is connected to the main relay in parallel, the precharge device charging the capacitor of the motor controller in an initial stage of supply of the electric power, wherein the precharge device is turned off after charging the capacitor a predetermined capacity, and the main relay is turned on so that a power current is supplied to the driving motor, and wherein the precharge device has an intelligent-power switch unit mainly comprised of an electric-power-supply control unit including a main MOSFET serving as a semiconductor switching device.
In the above-described system, the precharge circuit including a mechanical precharge relay and a charge resistance is omitted, and the intelligent-power switch unit mainly comprised of the electric-power-supply control unit including the one-chip semiconductor switch device, such as the MOSFET etc., is connected as a substitute for the precharge circuit. Thus, the size and the cost of the system are effectively reduced. Moreover, damage of the motor controller caused due to a rush current which flows when electric power has been supplied can be prevented.
Further, according to the second aspect of the present invention, it is preferable that the electric-power-supply control unit includes the main MOSFET which is capable of limiting an electric current, a first reference circuit which is connected in parallel to the main MOSFET, generates a reference voltage for detecting overcurrent which flows in the power supply line, and outputs an abnormality detection signal generated owing to the overcurrent, a second reference circuit which is connected in parallel to the main MOSFET, generates a reference voltage for detecting undercurrent which flows in the power supply line, and issues an alarm to an outside by outputting an abnormality detection signal generated owing to the undercurrent as a monitor signal, a charge pump circuit which raises an output voltage from the power supply in a state that a switch corresponding to the load is switched on, and outputs a voltage raised as a drive voltage, and a drive circuit which makes the main MOSFET turn off by supplying the drive voltage supplied from the charge pump circuit to the main MOSFET when the drive circuit receives a low-level signal from the first reference circuit in response to the abnormality detection signal indicating the overcurrent. When abnormal overcurrent caused from, for example, short circuit, has been detected, the main MOSFET is turned off. When abnormal undercurrent caused from, for example, opening, has been detected, the monitor signal is output to issue an alarm to the outside. Thus, the power supply line and the foregoing system units can be protected. The operations, which must be performed in the event of the abnormality, are performed with satisfactory response to correspond to the overcurrent, the undercurrent or the overheat.
Further, according to the third aspect of the present invention, it is preferable that the first reference circuit includes a first comparator which inverts a high level signal generated in response to the abnormality detection signal indicating the overcurrent into the low level signal, and outputs the low level signal to the drive circuit, and a second comparator which inverts a low level signal generated in response to the abnormality detection signal indicating the undercurrent into a high level signal, and outputs the monitor signal. Since the first and second comparators are respectively provided for detecting the overcurrent and the undercurrent, the response for the detection of each abnormality can be effectively improved, and therefore, the reliability can be improved.
Incidentally, according to the second aspect of the present invention, the electric-power-supply control unit is capable of limiting overcurrent. The current limiting function of the electric-power-supply control unit is apparent from a region (A) shown in FIG. 4 (described later).
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments when read in conjunction with the accompanying drawings.